Snap switch overtravel mechanism



July 18, 1944.

0. HIKAMINKY SNAP SWITCH OVERTRAVEL MECHANISM Filed Dec. 31, 1942 could not be used in Patented July 18, 1944 2,354,027 f SNAP SWITCH! OVEBTRAVEL MECHANISM- Oscar-Ell aminky Micro Switch Corpora I poration of Illinois; I

., MP. 111., usignor to tion, Freeport, 111., a cor- Application'neceinber 31. 1942, Serial No. 470,789 7 Claims. (Ci. zoo-4'1) This invention relates to electric snap switches of the small, compact, precision type shown in McGall Patent 1,960,020, issued May 22, 1934, and is more particularly concerned with an improved overtravel mechanism.

In referring to, the switch of my invention as a "precision switch, it must be understood that this means one which operates in response to very slight movement of the. operating plunger, and one'which is intended to operate consistently at the same position of its plunger. One commercial construction or the switch, for example, hasi the switch mechanism in a molded sulating material, occupying less than one and one-half (l /2) cubic inches. of space, and operating inresponse to a plungerrmovement of the order of one ten thousandth (0.0001) inch between on and on with only a few ounces of operating force, although con'trblling directly loads of the order of a thousand watts onalternating current.

housing of in Provision for overtravel is'important inswitches.

of this kind, because in the location 01 the switch with respect to the device or member which must operate it in application importance, and in allicases the provision for over-,- travel guards the switch vmechanism against damage from accidental or other occasional excess movement or the device or member operating the switch. 'An outstanding travel mechanisms devised heretofore has,v been that the overall height of the switch'is increased, all out 01' proportion, by the addition of the overtravel mechanism, the mechanism in many instances having an overalldimension almost equal to, if not even greater than, theoverall heightoi the switch itself. As a result, switches so equipped; places. where only, limited space was available, as, for example, where switches are mounted in instruments. It is, there, fore, the principal object oi my invention to provide a switch in which the .overtravei assembly,

is incorporated inside the switch between the intemal operating plunger and the external actuated plunger, whereby the overall height or the switch is reduced appreciably and other important.

advantages are also realized, such as, t (1) The decreased weight 01' the assembly, which makes it more responsive to rapid-actuation because of the lower inertia factor, and

(2) Reduced side thrust, which is duetothe decreased length or the plunger and results in smoother and easier where precise operation islnot of prime 7 operation, because of. the decreased frictional resistance to movement.

it permits greater tolerance Another objectis' to provide a switch of the v kind ine'ntioned,in which the outer end 01" the external plunger, whichis made of hardened steel for reduced wear, is rounded to provide smooth easyoperation when actuated directly by sliding contact, the plunger being, moreover, freely rotatable with respect to the overtravel mechanism, so-that wear is-not apt to occur all at one point. The combination of the rounded contour and the stubbiness of the external plunger reduces the effect of side'thrust to a minimum and makes the v mechanism highly responsive.

The invention is illustrated in the accom panyingdrawing,,in which Figure 1 is a longitudinal section through a switch made in accordance with my invention,

onanenlarged scale;

2 is another longitudinal section showing the parts in moved positions, at the operating point or the switch;

Fig. 3 is another longitudinal section with the parts moved farther so as to illustrate the overtravel, and

Fig. 4 is a top view of the switch withthe cover removed so as to show the relationship or themternal and external plungers to the snap action spring. V I

The same reference muneralsare applied to corresponding parts throughout the views.

obj'ection to the overa the U-shaped anchor H.

The switch comprises a housing 6 of insulating material consistingof a base land a cover 8 for enclosing the switch mechanism. 9 is a metal insert in the base carrying a'screw l0, and I l is an anchor heldrby' the screw. The insert 9 provides an electrical connection between the anchor ii and an external terminal'screw l2. The anchor ll supports a pair of compression spring members 13 and a tension spring member ll of the snap mechanism oithe switch. The two side compression members l3 and the central tension member I of the snap mechanism'are stamped integrally from a single sheet of thin spring material, so

that the several spring members togetherconstitute a three-pronged piece l5. This piece carries a movable contact it which, when the'switch operates, moves with snap action" between the stationary contacts I! and II on the base. The stationary contacts 11 and l8-each have a screw ll mounting the same on another metal insert 20 in V the base 'I which provides an electrical connectionlbetween the contact H or I 8 and an external terminal screw 2 l.-

The compression members l3 are pivotally supported in notches 22 in the ends of'the legs of The tension member I4 is supported in cantilever fashion under the head of the screw l at the base of the U of the anchor H and passes near the pivotal axis of the two compression members I3 in the notches 22. If pressure is appliedto the tension member l4 to deflect its tension center line across the pivotal axis of the two compression members l3, the spring members l3 and I4 will coact to snap the movable contact II from its one extreme position to' the other. When the tension member i4 is forced down, the movable contact i3 is snapped out of engagement with the contact H, the snap action member i3 coming into engagement with the contact it, but when the pressure is released, the contact l3 snaps back be understood, therefore, that Figs. 1-3 are in tended only to show the general relationship 0 the parts mentioned.

Th operating plunger 23 is similar to that forming the subject matter of a copending application of Arthur L. Riche and Ben J .Rush serial No. 448,598, filed'June 26, 19.42, and includes a highly polished stainless steel pin 24 onto which is molded a head 23 of insulating material. The r switch, as will soon appear, is operated bydepressing the head. 25 so as to deflect the tension member l4 downwardly to operate the switch. The pressure is applied to the tension member l4 by a central spherical projection 21 on the bottom of the head 23 Ma point between the point of support of the tension member under the head of the screw in and the point of support of the compression springs i3 in the notches 22. The head 23 overhangs the two legs of the anchor ll has an easy working fit, so that the plunger 39 may be reciprocated freely with respect to the collar 32 and pin 24 in the overtravel movement. The inner end of the plunger 33 has an annular flange 4|, which when the switch is at rest engages the bottom of the ferrule 33 to prevent upward displacement of the plunger 39. The outer end of the plunger 39 is substantially spherical, as indicated at 42, so that the plunger 33 may be operated smoothly directly by sliding engagement with a member or members movable with respect to the switch in a direction transversely with respect to the axis of the plungers 23 and 39. The plunger 33 is preferably of hardened steel to. reduce wear and will turn with respect to the collar 32 to distributewhat little wear is apt to occur. The collar 32 is preferably, although not necessarily, of cadmium plated brass, while the washer 33 may be of brass or any other suitable material.

In operation, when the plunger 39 is depressed, the operating plunger 23 moves with it as a unit," as shown in Fig. 2, so as to deflect the tension member i4 downwardly and operatethe switch. The plunger 23 moves with the plunger 39 as a unit in the snap action of the switch because of the preloading of the spring 34, the preloading being great enough to insure that the spring will not be further compressed except in the overtravel movement after the snap operation of the switch. The movement of the plunger 23 is limited by engagement of the head 23 with the two legs of the anchor II, 'as shown in Fig. 3, the movement being limited to a little more than that necessary to deflect the tension member l4 to the point at whichit moves with snap action to the opposite extreme position. When the operating plunger 23 is stopped by engagement with the anchor I i, the spring 34 will yield so as to allow so that the anchor serves as a stop to limit the j downward movement of the plunger, the'movement being limited to a little more than that necessary to deflect the tension member H to the point at which it'moves with snap action to theopposite extreme position. The head 23 is of generally cylindrical form but has a star-shaped overtravel of the plunger 39, the washer 33 in the overtravel being forced downwardly away from the collar 32 by the plunger 39. thereby compressing the spring 34 between the washer 33 and the head 23,as clearly appears in Fig. 3.

- It should be clear from the foregoing that the overtravel assembly of my invention is incorskirt portion 29 formed thereon intermediate the endsthereof ina plane substantially normal to housing will prevent rotation of the plunger with no perceptible increasein the resistance to the movement of the plunger.

The 'pin 24, in accordance with my invention;

has a collar 32 suitably fixed on the upper end portion thereof, as by a press fit, and this collar serves both as a limiting abutment and retain ing means for a washer 33 loosely mounted on the pin 24 and a conical or beehive spring 34 which encircles the pin 24 with its large end seated on top of the enlarged skirt portion 23 of the head 23 and its small end engaging the underside of the washer 33, as most clearly appears in Fig. 1. The spring is held caged between the head 23 and washer 33 under a certain preload compression. A one-piece metal ferrule 33 entered through a hole 33 in the cover 8 has its lower portion swedged outwardly, as indicated at 31, to fasten the ferrule permanently in place on the cover. The ferrule provides a guide 33 therein for an external plunger 39. The plunger 39 has a bore 43 in which the collar 32 porated inside the switch between the internal operatingplunger 23 and the external actuated plunger 33, and in that way the overall height of the switch is reduced appreciably. Furthermore with this improved construction, the weight of the assembly is decreased, which makes'it more responsive to rapid actuation, because of the lower inertia factor. Then. too, there is reduced side thrust, which is due to-th'e decreased length l of the plunger 39, so that smoother and easier operationis obtained because of the decreased frictionalresistance to movement. It should also be clear that the combination of the rounded contour v42 and the stubbiness to the external plunger 39 reduces the effect of side thrust to a minimum and makes the mechanism highly responsive.

It is believed the foregoing description conveysa good understanding of the objects and advantages of my invention. The appended claims have been drawn to cover all legitimate modifibeing movable with snap action from one extreme position to another for switch operation when pressure is applied to a portion of said element,

an operating plunger in said housing guided for reciprocatory movement with respect to the housing and engaging said switch element to apply pressure thereon, an external actuating plunger also guided for reciprocatory movement with respect to the housing, a pin movable with one of said plungers and projecting therefrom into the other of said plungers and guided therein for reciprocatory movement with respect thereto, means in said housing for positively limiting movement of the internal plunger toward the switch element, and a coiled compression spring encircling said pin inside the housing for yieldably and resiliently transmitting pressure from the external plunger to the internal plunger, said spring being arranged to yield to permit overtravel of the external plunger when movement of the internal plunger is stopped.

2. A device as set forth in claim 1, wherein the coiled compression spring is substantially conical in form so as to permit compression thereof down to a small dimension, the large end of the spring being seated on the internal plunger and the small .end thereof being operable by the ex ternal plunger.

3. In a device of the character described, the

combination of a housing, a switch element comprising a thin, leaf spring. snap action switch member operatively supported therein, one end being movable with snap action from one extreme position to another for switch operation when pressure is applied to a portion of said element, an operating plunger in said housing guided for reciprocatory movement with respect to the housing and engaging said switch element to apply pressure thereon, an external actuating plunger also guided for reciprocatory movement with respect to the housing, a pin movable with one of said plungers and projecting therefrom into the other of said plungers and guided therein for reciprocatory movement with respect thereto,

'means providing an annular shoulder on the outer end portion of said pin, a washer reciprocable on the pin toward and away from said shoulder, and a coiled compression spring within said housing encirclingthe pin and heldcaged under a predetermined preload compression between the washer and the plunger movable with the pin, whereby to transmit pressure from the external plunger to the internal plunger yieldably and resiliently.

4. A device as set forth in claim 3, wherein the coiled compression spring is substantially conical in form so as to permit compression thereof down to a small dimension, the large end 01' the spring being seated on the internal plunger and the small end thereof having engagement with the washer.

5. In a device of the character described, the combination of a housing, a switch element comprising a thin, leaf spring, snap action switch member operatively supported therein,'one end being movable with snap action from one extreme position to another for switch operation when pressure is applied to a portion of said switch element, an operating plunger in said housing guided for reciprocatory movement with respect to the housing and engaging said switch element to apply pressure thereon, an external actuating plunger also guided for reciprocatory movement with respect to the housing, a pin movable with one of said plungers and projecting therefrom into the other of said plungers and guided therein for reciprocatory movement withrespect thereto, means providing an annular shoulder on the outer end portion of said pin, a washer reciprocable on the pin toward and away from said shoulder, and a coiled compression spring within the housing encircling the pin and held caged under a predetermined preload compression between the washer and the plunger movable with the pin, whereby to transmit pressure from the external plunger to the internal plunger yieldably and resiliently, and means for positively limiting movement of the internal plunger toward the switch element, said spring due to its preload compression being arranged to yield only when movement of the internal plunger has been positlvely'stopped, whereby to permit overtravel of the external plunger.

6. In a device of the character described, the combination of a housing, a switch element comprising athin, leaf spring, snap action switch element operatively supported therein, one end thereof being movable with snap action from one extreme position to another for switch operation when pressure is applied to a portion of said element, an operating plunger in said housing guided for reciprocatory movement with respect to the housing and engaging saidswitch element to apply pressure thereon, a pin projecting from said plunger and reciprocable therewith, a coiled compression inside the housing spring surrounding said pin and seated on the plunger, a washer reciprocable on the pin and seated on the outer end of the'spring, a collar adjustable on the outer end portion of the pin toward the washer serving to hold the spring cagedunder a predetermined preload compression, a removable cover for said housing, and an external plunger reciprocably mounted in said cover and having a bore therein, the collar on the outer end portion of said pin 7 being guided therein for reciprocatory movement of the external plunger with respect to the internal plunger, said external plunger being. ar-

ranged to engage the washer to transmit movement to the internal iently through the medium of the coiled compression spring.

7. A device as set forth in claim 6, including means in the housing for positively limiting movement of the internal plunger toward the switch element, said spring being arranged to yield when movement of the internal plunger is positively stopped, whereby to permit overtravel movement of the external plunger.

OSCAR. H. KAMINKY.

plunger yieldably and resil- 

